(1) Field of the Invention
The present invention relates to the field of sonar sensors and in particular to towed, active sonar arrays.
(2) Description of the Prior Art
Although passive (receiving) towable sonar arrays have become refined technology, active (transmitting) arrays, because of the requirement that the active array be positioned in a vertical position, to achieve vertical aperature have presented certain drawbacks. Typical conventional active systems are mounted in hard, typically large, rigid towed bodies, for example, the current AN/SQS-35 tow body. The tow body is required to maintain the active array in a proper vertical orientation in order to provide the required acoustic pattern.
Conventional towed active sonar systems are large, cumbersome, and require expensive handling systems that use a substantial amount of space aboard a surface combatant. Depending on the frequency of the transducers, the hard, towed bodies are quite large and difficult to handle, frequently weighing up to 4000 pounds or more. Additionally, the handling equipment needed to deploy and recover such a tow body requires considerable deck space on the aft end of the ship and this equipment can increase the radar cross-section of the ship.
These types of handling systems impose limitations on the maneuverability of the tow vessel, prevent the covert deployment of the active array, and are unwieldly and dangerous for deployments or recoveries during high sea states.
In an attempt to solve many of the problems discussed above, soft-bodied towable devices have been developed. These soft-bodied devices 60, FIG. 1, along with a towed receiver array 62, are attached to the vessel 100 via the towing cable 64, as described in U.S. Pat. No. 6,088,293, which is incorporated by reference as if fully set forth herein. However, known soft-bodied devices 60 suffer from several problems.
A disadvantage of these known devices is that the single soft-bodied device 60 transmits at only one depth D within a water column, and as a result, in only a single water layer 70. The depth of the water layer 70, 72 depends on numerous factors including, but not limited to, overall water depth, salinity, environmental characteristics, and water currents. The boundary of the layer tends to reflect the acoustic signals 74, create “shadow zones” or areas where submarines and the like can hide without being detected, and reduce the performance of the sonar system.
Accordingly, what is needed is an active transducer array that can be deployed from a ship in a manner similar to the deployment of passive transducer arrays, such as paying out through a hull-mounted port. The active transducer array should also be capable of simultaneously operating at various depths such that the system may ensonify the entire water column to optimize the distribution of acoustic energy for the particular environment, including the various water layers 70, 72. Moreover, the tow cable should minimize the hydrodynamic drag forces.